1. Field
The present invention relates to a crystallization apparatus and method which prevent cracks from being generated.
2. Description of the Related Technology
Active matrix (AM) type organic light emitting display apparatuses generally include a pixel driving circuit in respective pixels. The pixel driving circuit typically includes a thin film transistor (TFT) formed using silicon. Amorphous silicon or polycrystalline silicon may be used as the silicon constituting the TFT.
TFTs constituting amorphous silicon (a-Si TFT) include a semiconductor active layer constituting a source, a drain, and a channel formed of amorphous silicon, and the amorphous silicon TFT has low electron mobility. Polycrystalline silicon TFTs generally have high electron mobility and superior light irradiation stability when compared to the amorphous silicon TFT. Thus, polycrystalline silicon TFTs are well adapted for being used as an active layer of a driving and/or switching TFT of an active matrix organic light emitting display apparatus.
The polycrystalline silicon TFT may be manufactured using various methods. Examples include a method in which polycrystalline silicon is directly deposited and a method in which amorphous silicon is deposited and crystallized. The method for depositing the polycrystalline silicon may include a chemical vapor deposition (CVD) method, a photo CVD method, a hydrogen radical (HR) CVD method, an electron cyclotron resonance (ECR) CVD method, a plasma enhanced (PE) CVD method, or a low pressure (LP) CVD method.
The method in which the amorphous silicon is deposited and crystallized may include a solid phase crystallization (SPC) method, an excimer laser crystallization (ELC) method, a metal induced crystallization (MIC) method, a metal induced lateral crystallization (MILC) method, or a sequential lateral solidification (SLS) method.
The SPC method is typically performed at a temperature greater than about 600° C. for a long time, and its practicality may thus be significantly reduced. The ELC method may realize low-temperature crystallization. However, since a laser beam is expanded using an optical unit, uniformity may be deteriorated. The MIC method includes depositing a metal thin film on a surface of amorphous silicon to crystallize the amorphous silicon using the metal thin film as a catalyzer, and a crystallization temperature may thus be reduced. However, since polycrystalline silicon is contaminated by the metal, characteristics of a TFT device including a silicon layer formed by MIC may be deteriorated. Also, formed crystals may have a small size and the crystals may be distributed in a disorderly manner.